The invention is a method for braking a vehicle which includes having a drive motor, a hydrostatic drive unit and adjustable hydraulic machines, and an electronic subassembly that controls adjusting devices for the hydraulic machines. machines.
In the method the drive motor provides a braking moment to decrease the vehicle speed by continuously adjusting the hydraulic machines. For example, a diesel engine sill decelerate a moving vehicle when the accelerator pedal setting of the engine is reduced since this will reduce the engine speed. The braking moment of the diesel engine depends upon the ratio between the rpm of the engine and the rpm of the vehicle wheels. Thus, in order to increase the braking movement of the engine, the ratio must be changed. This is accomplished, for example, by changing from the fourth gear of a mechanical gear box to the third gear. For a vehicle having a hydrostatic transmission, it is necessary to adjust the hydraulic machines by swinging in the hydrostatic pump, i.e., reducing its stroke volume, or by swinging out the hydrostatic motor, i.e., increasing its stroke volume, or by making both of these adjustments.
It is known to utilize the braking moment of a drive motor, e.g., a diesel engine, to brake a vehicle by controlling adjustable hydraulic machines with an electronic subassembly so that a temporary transmission change inside of the hydrostatic drive unit to decrease the speed of the vehicle. For example, in a conventional hydrostatic drive unit with a primary control, i.e., with an adjustable hydraulic axial piston pump, and a constant hydraulic motor with the pump adjusted to the full-load setting, the maximum angle of traverse is controlled so that the angle of traverse is returned within a specific time to a minimum value or to zero. The length of the time interval between the maximum angle of traverse and the minimum value or zero determines the intensity of the braking, provided the braking moment of the drive motor is sufficient to stop the vehicle. A relatively short interval causes rapid braking, while a longer interval results in slower braking.
When the braking moment of the drive motor is no longer sufficient to assure a decrease in vehicle speed, additional braking will be required by the manual actuation of an additional brake by the vehicle operator. This may be necessary in rapid braking or in traveling downhill in order to prevent the drag moment exerted on the drive train by the vehicle, which can in such a situation far exceed the braking moment available from increasing the rpm of the drive motor and the hydraulic machines.
If operator intervention is unavailable, both the hydraulic machines of the hydrostatic drive unit and the drive motor will become overloaded and damaged.
The invention provides a method for braking a vehicle that renders the manual actuation of an additional brake by the operator unnecessary and prevents overspeeding of the drive motor.